It's somewhat common to render new content that, itself, will want to be able to update the same zone, but the client-side id can't be recalculated on the server side due to the nature of rendering and id allocation. Thus, the only way for the server side to know what the client-side id is, is for the client-side to pass that information along.
In my case, I'm working on a dynamic edit component that shows some content, with a link to switch to edit mode. Clicking the link updates the Zone with a form. Submitting the form needs to return the component back to its initial output-only state (but with the new content). At each step, the id of the Zone needs to be passed along so that the form, or output content, can render the correct content.